JPS6033525A - Light beam scanning system - Google Patents

Abstract

PURPOSE:To obtain a compact beam scanning system which scans plural beams by making one light beam into plural parallel light beams through an acousto- optic element and an optical lens, and directing them to a photosensitive medium surface through one ftheta lens and a couple of reflecting mirrors. CONSTITUTION:A laser beam emitted by a laser light source 1 is incident on the acousto-optic element 2. The element 2 is applied with signals 3 and 4 modulated with dichroic video signals for printing through an adder 13. Dichroic beams A and B for printing projected by the element 2 are made into parallel beams through the optical lens 5, and they are reflected by a rotary polygon mirror 6 and converged onto the surface of the photosensitive drum 12 through the ftheta lens 7 and couples of reflecting mirrors 8 and 9, and 10 and 11. Consequently, the compact beam scanning system which scans plural beams is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a light beam scanning method, and more specifically,
The present invention relates to a light beam scanning method suitable for an electrophotographic multicolor printer that prints characters, images, etc. on a photosensitive drum by directing a laser beam onto the photosensitive drum.

So-called electrophotographic laser printers print (record) information such as characters and images on a photosensitive drum by directing a laser beam onto the photosensitive drum. It is widely used as an output device for e-machines, facsimiles, and other terminal printing devices.

Conventionally, such laser printers have typically printed only one color, such as black, but as information becomes more diverse, there is a strong demand for multicolor printing, and several methods have been developed.
For example, two-color printers are now being considered.

In such a two-color printer, it is necessary to direct two laser beams corresponding to the number of colors onto the photosensitive drum surface from the normal direction thereof and to scan the photosensitive drum in the direction of the rotation axis of the photosensitive drum. Moreover, in the case of electrophotographic printers, the distance between the two beams on the photosensitive drum surface is considerable, in some cases hundreds of millimeters, because a charger or the like is installed between them. need to be maintained.

When directing two laser beams at a considerable distance apart, two identical optical systems are usually used. However, in this case, not only the scanning separation becomes large-sized, but also the cost of the apparatus increases.

In addition, it is difficult to adjust the positional relationship between the two optical system phases 17.
T, yes. Furthermore, since it is difficult to prepare two light sources with exactly the same characteristics, there is also a drawback that characteristics vary between beams.

Another method is to use only a laser light source as described in Japanese Patent Application Laid-Open No. 58-23058 (2005).
Use 1), use 1 optical element for each beer.
There are some that are made to look like this. This method is described in J-Description 1. /
I knee,, compared to the 6th type, it's a Kombaku 1~.

However, since two light sources are still used, variations in the characteristics (?l) between the beams cannot be eliminated.Also, it is difficult to adjust the position between the two light sources. Since the beam will be obliquely incident on the installed f/θ lens, 1/1 of the straight line of scanning will be lost.To prevent this, install a cylindrical beam between the scanning mirror and the f/0 lens. You can place a lens (a semi-cylindrical lens) so that the two beams are parallel to the beans, but if you do that, you will have problems adjusting the position of the cylindrical lens and deterioration of the beam characteristics. .

On the other hand, monochromatic laser printers that use the so-called multiple beam simultaneous scanning method use a single laser light source, and use an acousto-optic device to split the beam emitted from the light source into multiple beams. A plurality of beams are directed directly onto the photosensitive drum surface and scanned using one scanning mirror and one f.theta. lens. However, in this method, the distance between the beams is about 0.1 mm+ at most, and if you try to force them apart, the direction of beam orientation will no longer be normal to the photosensitive drum surface, resulting in distorted printing.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art, and to be able to scan the surface of a photosensitive medium by directing a plurality of beams from the normal direction to the surface and at positions separated from each other by several tens of man. , and provides a compact optical beam scanning system.

In order to achieve the above object, the present invention uses a method in which a plurality of light beams are directed to the surface of a photosensitive medium from the normal direction and scanned, and one light beam emitted from one light source is used. A light beam is formed into a plurality of mutually parallel light beams 11 using an acousto-optic element and an optical lens, and the plurality of light beams are made to enter one f/θ lens through one scanning mirror. Further, a light beam scanning method is provided in which each light beam emitted from the f/θ lens is directed toward the surface of a photosensitive medium using a pair of reflecting mirrors placed opposite each other at η.

To explain formula 1 of this invention in more detail, the drawings are as follows:
An example in which the method according to the present invention is applied to a two-color printer is shown below.
It's a creature.

In the drawing, the laser beam emitted from the laser light source 1 is
First, the light enters the acousto-optic element 2. This element 2 receives a signal 3.4 obtained by modulating two types of high-frequency 4V rear signals for two colors, for example, black and red, with video signals for black and red printing, respectively, through a 5- adder 13. The beam is diffracted into two beams corresponding to each color, namely beam 8 for black printing and beam B for red printing. The undiffracted light 14 is cut by a shielding plate 15.

The two beams A and B are then made incident on an optical lens 5. This optical lens 5 is installed at a position separated from the acousto-optic element 2 by its focal length. Therefore, beams A and B exiting this optical lens 5 are parallel to each other.

Two beams A1B emitted from the optical lens 5 are both scanned by a rotating polygon mirror 6. This scanning direction is
This is the direction of the rotation axis of the photosensitive drum 12, which will be described later.

Behind the rotating polygon mirror 6, there is a so-called f.theta. which ensures that the scanning speed of each beam on the surface of the photosensitive drum 12 is the same at any position and prevents the printed characters from being distorted.
A lens 7 is arranged.

The beams A and B that have passed through the f/θ lens 7 are directed to a pair of reflecting mirrors 8.9 and 10, 6-11 arranged opposite to η, and are directed toward the surface of the photosensitive drum 12 (I, -) C1 from the normal direction thereof. They were called separately to 111. At this time, the two beams Δ and B are connected to a pair of antifills placed opposite to each other at n.
It8.9JLJ2hi10.11, several tens++ on the photosensitive drum 12 surface in its rotational direction (arrow direction)
A distance of +m is maintained. Note that the reflecting mirrors 8.9 and 10.11 are installed so that the optical path lengths of the beams A and B from the f·θ lens 7 to the surface of the photosensitive drum 12 are equal. In other words, the optical path lengths of the beam A1B from the acousto-optic element 2 to the photosensitive drum 12 are both equal.

In addition, red beam B is 1 hour T compared to black beam A.
DA L-) Lij and directed. This time T is (Ct,
This is the time it takes for Fl to move to the directional position of the red beam B, and is determined according to the rotational speed of the photosensitive drum 12.

In 1-, C has been described for the case where there are two beams and two-color printing is performed, but it can be configured in exactly the same way if there are three light beams.

That is, in this case, three types of signals are input to the acousto-optic element, and another silk reflecting mirror is placed behind the f/theta lens. In this way, printing in three colors becomes possible.

As explained above, since the method of the present invention uses only one light source, unlike the conventional method that uses multiple light sources, it causes variations in characteristics between beams. do not have. Furthermore, it is naturally not necessary to prepare two light sources with the same characteristics.

Furthermore, since the method of the present invention uses a common optical lens, scanning mirror, and f/theta lens for each beam to direct a plurality of beams toward the surface of the photosensitive medium, the light source and optical system are not required. It is much more compact and the equipment cost is lower than the above-mentioned conventional system in which a plurality of devices are provided. Further, there is no need to adjust the positional relationship between the optical systems.

Furthermore, since the method of the present invention changes the optical path of each beam emitted from the f/theta lens using a pair of reflecting mirrors arranged opposite to each other, the beams do not overlap each other on the surface of the photosensitive medium. The distance between the mirrors can be increased, and the distance can be easily changed by changing the angle of deflection of the reflecting mirror.

Zaraniil: k, the method of this invention uses an optical lens! <2 beams parallel to j are incident on the scanning mirror, in other words, for 1·θ1 nonce, each beam is incident obliquely by 80·1 x parallel to its optical axis (since 7) , iI'i line 1/1 of 1 house. h< UJ1 harmed 4r
stomach.

[Brief explanation of drawings]

The drawings show one embodiment of this method.
FIG. 3 is a schematic perspective view showing a case where the present invention is applied to a two-color printer. 1: Shi - Rei) 11 Study on river (2: Acoustics) 3.4: Signal 5: Optics 1 nons 6: Rotating polygon mirror (scanning mirror) 7: r・θ1 nons 8.9.10.11 :Reflector 12: Sensitive) and Drill (photosensitive medium) One- 13: Clamping device 14: Non-diffracted light 15: Shielding plate Patent applicant Toshi Co., Ltd. 10-

Claims (1)

[Claims] A method in which multiple light beams are directed and scanned from the normal direction to the surface of a photosensitive medium, and a single light beam emitted from a single light source is scanned using an acousto-optic element and an optical lens. Create multiple light beams that are parallel to each other, make these multiple light beams pass through one scanning mirror and enter one f/θ lens, and then each light beam emitted from the f/θ lens , a light beam scanning method that uses a pair of anti-copper mirrors placed opposite each other to direct the light beam toward the surface of the photosensitive medium.